Papers by Keyword: Flow Behaviour

Abstract: In cold bulk metal forming, coatings based on zinc phosphate are commonly used for lubrication. This has a negative impact on the environment, negatively affects human health, and requires significant pre-and post-surface treatments. Powder metallurgical (PM) components are a promising alternative to zinc phosphate coatings due to the process related porosity of the workpiece which acts as lubricant reservoir. During the forming process, the lubricant stored in the pores is released and lubricates the tool and workpiece surfaces. For an efficient process design of such components, finite element method (FEM) is an effective tool to analyse forming and friction behaviour. To this end, a realistic material model is essential for accurate simulation results. Hence, in this work, the flow behaviour of PM semi-finished products is characterised by means of compression and tensile tests. The results indicate that the material exhibits different behaviour under compression and tension. In compression, the material demonstrates higher yield strength and flow stresses compared to tension. Additionally, inhomogeneity of the material distribution can be observed, characterised by a denser core and more porous outer regions. The porous outer regions make it suitable for storing lubricant for application in forming processes.

Abstract: Fused deposition modeling (FDM) has been developed to adapt more application with a wide variety of material used, especially metal filled PLA filament. However, choosing wrong PLA-based filaments’ process parameters is a popular situation that causes great product’s dimensional error. This research is focused on studying the difference in the input velocity parameters between PLA and PLA-copper filament. This paper presents a numerical nozzle model and use finite element analysis method to investigate the melted filament fluid behavior. Flow parameters such as pressure, melting temperature range and velocity were discussed in detail. Experiments were then carried to determine optimal printing velocity range of the two filaments. Results show that the filament input velocity has great influence on flow parameters as this velocity changes, the flow parameters change as well. Finally, based on the evaluation of dimensional accuracy of printed samples, the optimal input velocity for each type of filament has been found, which are 2 – 3.5 mm/s for PLA and under 5 mm/s for PLA-copper.

Abstract: The blends of Nylon 6/Acrylonitrile-Butadiene-Styrene (ABS) with styrene-maleic anhydride (SMA) was prepared by melt blending as the compatilizer. Mechanical properties, dynamic mechanical analysis (DMA) and fracture appearances were determined. It was found that the impact and tensile strength firstly increased and then decreased along with the increase of the SMA content. The properties reached maximum values when the content of SMA was 1.5%. The results of DMA and scanning electron microscope (SEM) indicated that the addition of SMA can effectively enhance the compatibility of Nylon 6 and ABS. Key words: Nylon 6, ABS, SMA, blends, modification

Abstract: Rheological studies of polymers are of great importance in optimizing the processing conditions and in designing processing equipments like injection molding machines, extruders, and dies required for various products. Melt rheological studies give us valuable viscosity data that will be helpful in optimizing the processing conditions. Parameters like melt viscosity as a function of shear rate or shear stress and temperature have become more and more important. Previous study indicated that the flow behaviour of the compound depends on the filler loading. Lesser elastic torque was found with compound containing lower filler content as compared to higher filler content. In this work, effect of dual filler, based on Carbon Black / Silica filled Epoxidised Natural Rubber (ENR) compound was investigated. A total of 80phr of filler content based on passenger tyre tread formulation was used in the experiment. The compounds were prepared by melt mixing in tangential type of an internal mixer. The rheological and the processability properties of the compounds were determined using three different testing instruments namely Capillary Rheometer, Mooney viscometer and Rubber Process Analyzer (RPA). A variation of shear rates (ranging from low to high) was performed, in order to better reflect the actual processing condition in rubber manufacturing. It was found that ENR mix with ratio silica to carbon black 70:10 exhibited the best flow behaviour and processability properties as compared to control and other mixes.

Abstract: The flow curve behavior and microstructure evolution of commercially pure titanium (CP-Ti) through uniaxial hot compression was investigated at 850 °C and a strain rate of 0.1/s. Electron back scattered diffraction (EBSD) was employed to characterize the microstructure and crystallographic texture development for different thermomechanical conditions. The stress-strain curves of CP-Ti alloy under hot compression displayed a typical flow behavior of metals undergoing dynamic recrystallization (DRX), which resulted in grain refinement. The critical strain for the onset of DRX was 0.13 using the double differentiation analysis technique. It was also revealed that the texture was markably altered during hot deformation.

Abstract: Micro metal injection molding (µMIM) prior to conventional plastic injection molding (PIM) has become widely demanding due to its smaller size, more complex geometric surface and time consuming on its product. Metal and ceramic in powder form of various sizes up to µm is mixed with binder system to produce products that meet the requirements. Nano size yttria stabilized zirconia (YSZ) with average particle size of 25nm, was tested both physically and mechanically for its properties before mixing and injection process using several testing such as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), pycnometer density, critical powder volume percentage (CPVP) and rheology respectively. Grain shape for YSZ particle is near spherical with the diameter range between 21.2 – 33.5nm while the CPVP shows the highest powder loading was 41.4%. Binder system of 70% palm stearin and 30% polypropylene (PP) was then mixed with YSZ at 37%, 38% and 39% by using internal mixer with roller blade type. By using CPVP of 41.4% as the guideline, mixing was done beyond the critical point until it is capable of becoming the dough mixture and was found that 43% powder loading is the highest loading it can achieved. This dough form of every mixture of powder loading was crushed to obtain pellet size as the feedstock. Rheology test was carried out for each powder loading at 180oC, 190oC and 200oC with the load increasing from 10N to 20N to determine the plastic behavior and best relationship between viscosity (Pa.s) and shear rate (1/s). Dilatant flow behavior for all the powder loadings and smooth data distribution during testing at 180oC was observed respectively. Critical parameters involving in injection process such as mold temperature (oC), melt temperature (oC), pressure (bar) and time (s) was manipulated for every powder loading to obtain the best result with no defects such as shot and flashing. Each critical parameter increased gradually as the powder loading (%) increased. Debinding and sintering process will be carried out to determine the strength and toughness by using micro hardness and micro tensile test respectively.

Abstract: A simulation model for the filling of a tubular cavity during water assisted injection molding is proposed. The polymer melt and water are assumed to be incompressible and to follow a Hele-Shaw fluid behavior. The finite element/finite difference/control volume methods are adopted for numerical simulation of the melt front, pressure at injection location variation, water thickness fraction and bulk temperature about a curved pipe, the simulation results have good agreement with the results presented in the former experiment. In comparison with the simulation result of gas-assisted injection molding, water assisted injection molding can give parts with thinner and more uniform walls and more rapid cooling.

Abstract: The flow behaviors of molten Al alloy in sand mould cavity with varied gating system were simulated under vacuum counter-pressure casting and the ingate velocity was predicted using a software package. At same process conditions, the flow behaviors were investigated using electrode contact method. The comparison between the simulated results and the investigated results shows that a good agreement is achieved. The ingate flow velocity exceeding critical velocity and large velocity deviation are detected during filling mould withⅠtypes gating system, resulting in turbulent flow behavior. Whereas, flow behaviors take on stable flow pattern during filling the other mould cavity, although some differences of flow behaviors are present. The small ingate flow velocity and velocity deviation during filling mould cavity with Ⅲ type gating system may be conduce the more stable flow pattern thanⅡtype gating system.

Abstract: The flow behaviors under different filling pressures were observed using electrode contact method. The relationships of recorded time and related point location were analyzed and deduced in terms of the flow tendency. The flow behavior figures were plotted at different time according the relationship. It was found that the unstable flow pattern takes place because filling cross-sectional area changes abruptly from the flow behavior figures. According to energy conservation and mass conservation theory, the relationship of flow velocity and filling pressure was established. Combining this relationship and critical flow velocity, the judgment equation of critical filling pressure was achieved.

Abstract: The microstructural control of rolled products is based on managing the austenite phase transformations during and after hot deformation to attain the desired microstructure after the cooling step. Therefore, it is very important an appropriate description of the kinetics of the hardening and softening phenomena taking place during the deformation at high temperatures, namely, dynamic recovery (DRV) and recrystallization (DRX). This investigation examines the effect of manganese contents on the hot flow behaviour of plain carbon steels. For this purpose, uniaxial hot compression tests were carried out in carbon steels in an extensive range of temperatures, from 1123 to 1373 K and strain rates, from 510-4 to 110-1 s-1. This work is focused in determining the physically-based constitutive equations that govern the plastic behaviour of plain carbon steels. Experimental results were compared with the predictions of the model and an excellent agreement over a broad range of temperatures and strain rates was obtained.